GB2249510A

GB2249510A - Tapping threaded holes

Info

Publication number: GB2249510A
Application number: GB9119619A
Authority: GB
Inventors: Martin John Michael Murphy
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-09-14
Filing date: 1991-09-13
Publication date: 1992-05-13
Anticipated expiration: 2011-09-13
Also published as: DE69110682D1; GB9119619D0; WO1992004997A1; JPH06500505A; EP0548195A1; EP0548195B1; AU8506391A; US5435786A; GB2249510B

Abstract

A tap tool T having passageways 14, 15 for the supply of fluid under high pressure and at a low flow rate is used to form threads in the wall of a preformed hole 12 in a component 10 formed of an aggressive material e.g. a metal matrix composite. The tap displaces the ductile phase of the metal matrix, and no material is cut away. <IMAGE>

Description

2 24 9510 1 COMPONENT WITH THREADED HOLE The invention relates to the

threading of a hole in a component made of a material in which it is difficult to form an internal thread in the wall of the hole by known methods. Such materials include so-called metal matrix composites, which consist of a continuous metal phase reinforced with a disperse phase which may or may not be metal. The continuous phase may be formed of a metal such as aluminium, magnesium, titanium or an alloy based on any of these; the disperse phase may be in particulate, fibre or whisker form and selected from a wide range of materials such as silicon carbide, boron carbide, alumina, carbon, sand and other refractory fillers; wires of steel, copper or silver; and the like. A typical metal matrix composite comprises from about 10% to 40% by volume of silicon carbide in a continuous phase of an alloy of aluminium/magnesium/silicon or aluminium/copper or aluminium/lithium. Composites are of value because of lightness in weight coupled with strength and stiffness properties which are exerted even at high temperatures. Such composites can be made by a wide variety of techniques. The component may be a part useful in the automotive or aerospace, aeronautical or construction industries. Other materials in which it is difficult to form threaded holes include so-called aggressive metals which present a resistance to being worked, e.g. ductile steels, titanium, and the like, and non-metallic compositions 2 such as particle boards, fibre based or reinforced materials.

It is one object of this invention to provide a method of making a threaded hole in a component made of a material in which it is otherwise difficult to form a threaded hole by known method. The invention is based on the discovery that a cold forming tool such as a tap can be used to form the threads. This appears to be possible because under the conditions of this invention the distribution of the disperse phase allows the tap to displace the more ductile continuous phase so allowing thread forming parts of the tool readily to form the required threads.

According to the invention in one aspect there is provided a method of threading the wall of a hole in a component composed of relatively ductile material, the method comprising urging a cold forming tool having thread-forming means into the hole characterised by supplying pressure resistant lubricant fluid, thereby to form the threaded wall.

Preferably, the cold forming tool has spaced apart thread forming rings and the pressure resistant lubricant fluid is directed to flow under pressure between adjacent rings into the gap between the tool and the wall to be threaded. The fluid may be introduced intermittently or continuously, as required. In a preferred feature, the tool has a main passage for the passage of the fluid, branch passages leading from the main passage to 3 outlets at the junction of adjacent rings. Many proposals exist in the literature to cut threads in metal see e.g. US-A-4693646 and DE-A-3307555 and DE-UM-A-G89 01178 and to provide a bore so that a lubricant and/or coolant liquid may flow therethrough.

These disclosures are not relevant to this invention where the tool operates by displacing metal and not cutting it, i.e. there is no swarf. Such thread cutting devices cannot be used with the ductile or aggressive materials of which the components relevant to this invention are formed. It is also proposed in US-A 2807813 to use a fluteless tap to form internal threads in a borehole in a ductile material but no liquid is present when that device is used. In contrast, in the present invention, a tap is used in association with the pressure-resistant liquid to form the desired threads in a particularly efficient and advantageous way.

The tool is preferably made of a high speed steel, e.g. cobalt steel, the use of which in the context is considered to be totally unexpected.

The lubricant fluid, which may be a liquid or gas, is preferably supplied at relatively high pressure (say 1200 psi) and a relatively low flow rate. The fluid is preferably also temperature resistant and is most preferably an extreme pressure resistant lubricant such as a gearbox oil.

4 The tool may be advanced into a preformed hole with rotation and/or by a rectilinear motion.

our investigations have established that where the continuous phase of a metal matrix composite is a ductile material, e.g. aluminium, the regions of component which are free of the disperse phase still have that ductility despite the presence of the dispersed hard or refractory particles in the matrix. When a thread forming tool of the invention is urged into the hole, the continuous phase being ductile yields under the insertion force, allowing the threads to be formed in the hole wall accurately and efficiently. The urging is done cold by rotating the tap or by rectilinear motion. No material is cut away, so there is no swarf etc. to be removed. There is some evidence to suggest that the wall portions defining the formed threads have a high concentration of the hard particles, which may provide increased strength and wear resistance.

The fluid is required because if fluid is not present the tool is subjected to severe wear and will usually last for a single use only. The volume of fluid required is very low, which implies that only a thin film of material is formed between the wall to be threaded and the thread former, which film must have lubricous and pressure resistant properties.

In other aspects, the invention includes a component having a hole therein, the wall of the hole being threaded, the threads having been formed in the wall of a preformed hole by the urging therein of a cold forming tool having thread-forming means; and a cold forming tool comprising a shank having spaced apart thread forming rings, means being provided to supply pressure resistant lubricant fluid to outlets adjacent and/or between the rings.

In order that the invention may be well understood it will now be described by way of example only with reference to the accompanying diagrammatic drawings, in which:

Figure 1 is a section of a component having a hole with generally smooth walls showing the thread forming tap, and Figure 2 is a section of the threaded hole.

The component C comprises a body 10 formed of a metal matrix composite such as a ductile aluminium/magnesium/silicon alloy containing hard particles of silicon carbide 11 dispersed therein. A hole 12 having straight side walls is formed, e.g. by punching, drilling or the like into the depth of the body 10. A cold forming tool T in the form of a tap has thread former rings 13 which are spaced apart longitudinal of the shank. A passage 14 extends through the shank and has branch passages 15 which open at the outlets 16 at the junction, i.e. roots of adjacent 6 rings 13. A lubricant which is pressure and temperature resistant, e.g. a gearbox oil, is passed through the outlets 16 at relatively high pressure but low flow rate to be interposed between the walls of the hole 12 and the tool T. The rings are dimensioned according to the size of threads to be formed. The tap T is then urged into the hole 12 using known equipment and then removed. The insertion cause the particles of the silicon carbide to be displaced away from the hole wall because of the ductility of the continuous phase of the metal matrix composite.

The hole has thereby been threaded at 20 by the rings 13 and the body retains its properties of lightness in weight, strength, stiffness and the like. It is surprising that a metal matrix composite can undergo deformation during the tapping leading to the formation of threads without any adverse effect. There is evidence that the particles are concentrated in the formed threads 20. The fluid appears to act lubriciously to allow the tool to move relative to the hole wall and to provide a boundary layer to reduce tool wear. The fluid may however play a more direct role in shaping the thread as there is evidence to suggest that the fluid on the tap contours presents a mould surface which deforms the wall of the hole.

The invention is not limited to the embodiment shown. The tool may be fluted to allow for escape of fluid; the fluid may be introduced in other ways; the fluid may be nitrogen; the component may be made of metal or a gas such as non-metal. The 7 hole may be blind or a through hole

Claims

A method of threading the wall of a hole (12) in a component (10) composed of relatively ductile material, the method comprising urging a cold forming tool (T) having threadforming means (13) into the hole (12) characterised by supplying pressure resistant lubricant fluid, thereby to form the threaded wall.
2. A method according to Claim 1, characterised in that the cold forming tool (T) has spaced apart thread forming rings (13) and the pressure resistant lubricant fluid is directed to flow under pressure between adjacent rings (13) into the gap between the tool (T) and the wall of the hole (12) to be threaded.
3.

A method according to Claim 2, characterised in that the tool (T) has a main passage (14) for the passage of the fluid, branch passages (15) leading from the main passage to outlets (16) at the junction of adjacent rings (13).
A method according to any preceding Claim, characterised in that the fluid is supplied at a relatively high pressure and a relatively low flow rate.
C A method according to Claim 4, characterised in that the fluid is supplied under a pressure of about 1200 psi.
A method according to any preceding Claim, characterised in that the fluid is also temperature resistant.
7.

A method according to any preceding Claim, characterised in that the fluid is an extreme pressure resistant lubricant such as a gearbox oil.
8.

A method according to any preceding Claim, characterised in that the cold forming tool (T) is advanced into the hole (12) with rotation.
9. A method according to any preceding Claim, that the tool is a thread forming tap.

characterised in
10. A method according to Claim 9, characterised in that the tap is formed of a steel such as a high speed tool steel.
11. A method according to Claim 10, characterised in that the material of which the component is made is a metal matrix composite.
12. A method according to Claim 11, characterised in that the material comprises aluminium or the like as the continuous to phase of the matrix, and particles (11) of silicon carbon or like hard or refractory material are dispersed therein.
13. A method according to any of Claims 1 to 10, characterised in that the material of which the component is made comprises an aggressive metal, e.g. a steel.
14. A method according to any of Claims 1 to 10 characterised in that the material of which the component is made comprises a particle board.
15. A component (C) having a hole (12) therein, the wall of the hole (12) being threaded (20), the threads (20) having been formed in the wall of a preformed hole (12) by the urging therein of a cold forming tool (T) having thread-forming means (13) and means (14, 15) for the passage of a fluid therein under high pressure and a low flow rate.
16. A component according to Claim 15, characterised in that the component is made of a relatively ductile material.
17. A component according to Claim 15 or 16, characterised in that the component comprises a metal matrix composite.
A component according comprising aluminium as the to Claim 17, characterised by continuous phase and particles (11) of silicon carbide or like refractory material as the disperse phase.
19. A component according to Claim 15 or 16, characterised in that the component is formed of particle board.
20. A cold forming tool (T) comprising a shank having spaced apart thread forming rings(13), characterised by means (14, 15) to supply pressure resistant lubricant fluid adjacent and/or between the rings.
A tool according to Claim 20, characterised in that a main passage (14) for the fluid extends through the shank and branch passages (15) extend from the main passage to emerge at outlets (16) between adjacent rings.
22. A tool according to Claim 20 or 21 formed of a steel.

characterised by being
23. A tool according to Claim 22, characterised by being formed of a cobalt steel.
24. A tool according to any of Claims 20 to 23, characterised in that passages in the thread forming rings have been shaped by spark erosion.

1 \I-
25. A tool according to Claim 20 or 21, characterised in that the tool has been formed by powder metallurgy.